DESCRIPTION: An established researcher in the area of early vision proposes to use psychophysical and computational methods to study grouping, segregation, and contour integration in multi-element patterns. Specific aims include: 1) the measurement of pairwise trading relationships in grouping strength for symmetry (e.g. how does spatial proximity interact with symmetry in grouping tasks?) 2) comparison of filter vs. structure-based models of grouping and segregation 3) testing of different models of contour integration, 4) measurements of eccentricity effects in texture segregation, 5) modeling of the mechanisms of perceptual organization in perception of complex images. The bulk of the data will be collected with a three element display. The subject's task will be to determine if the center item groups more strongly with the left or right flanking item. In other tasks (e.g. section 4.2) Ss will identify the orientation of a texture patch. A model of grouping is proposed starting with filtering by simple cells as previously modeled by Albrecht and Geisler. A second, "transformational" matching stage allows for similar items to be grouped together. In a complex image, the plan is to have receptive field matching generate a first set of primitives that can be grouped. These groups are then subject to transformational mapping and higher-order groupings can be based on the results of that operation. Grouping is based on a variety of grouping rules (e.g. figure-ground grouping, associative grouping - a principle that holds that if A and B group and B and C group than A and C will group). The model asserts that grouping can be "multi-level" though it is admitted that "our current understanding of multiple-level grouping" is in a rather primitive state.